1. Field of the Invention
The invention relates to a driving force control device that controls driving force of a vehicle, or the like, and also relates to a driving force control method.
2. Description of Related Art
It is known that in an internal combustion engine installed on a vehicle, such as an automobile, there is a delay in response of its output or power to a driver's operation. In the case where the engine is equipped with a turbocharger, in particular, even if the accelerator pedal is depressed in an operating region in which the flow rate of exhaust gas is small, the engine is not sufficiently supercharged until the exhaust flow rate is increased and the rotational speed of a turbine becomes equal to or higher than a given speed. As a result, the output of the internal combustion engine, or the driving force of the vehicle, rises with a delay of several seconds.
If the response of the driving force to the driver's operation to depress the accelerator pedal is delayed, the driver may feel that the driving force does not follow his/her own operation, and stagnates (or remains substantially constant); therefore, the driver may get a sense of strangeness or discomfort when the driving force rapidly rises due to subsequent increase of the boost pressure. Namely, the driving force rises in steps in response to the operation to depress the accelerator pedal, whereby the response delay is emphasized.
In connection with the problem of the delay in response as described above, a driving force control device as described in Japanese Patent Application Publication No. 2010-24970 (JP 2010-24970 A), for example, determines whether a stagnation period for which the driving force stagnates (i.e., remains substantially constant), due to a delay in response is equal to or longer than a set period, and restricts subsequent increase of the driving force if the stagnation period becomes equal to or longer than the set period, so as to alleviate the driver's sense of strangeness or discomfort. If the stagnation period is less than the set period, on the other hand, the control device does not restrict the driving force, so as to assure high acceleration performance of the vehicle.
In JP 2010-24970 A, when the vehicle is rapidly accelerated with a large amount of operation to request acceleration, it is assumed that the driver is less likely or unlikely to care about a step or sudden rise in the driving force; therefore, the period of time for determining stagnation of the driving force is set to a relatively long period, and the driving force is less likely to be restricted. When the vehicle is slowly accelerated, on the other hand, it is assumed that the driver is likely to get a sense of strangeness or discomfort against a step or sudden rise in the driving force; therefore, the period of time for determining stagnation is set to a relatively short period, and the driving force is more likely to be restricted.